Starting in 1834 with the invention of the reaper, agricultural harvesting machines of the mobile type have used a reel to transport stalks of grain backward onto a platform as they are cut by the sickle bar.
In addition to reels, other types of crop-transporting mechanisms that have been used on agricultural harvesting machines include conveyor belts, augers, and pickup mechanisms.
In the era of horsedrawn harvesting machines, some, if not all, of the rotating mechanisms of the harvesting machines were driven by chains from a lugged wheel that supported the harvesting machine. Reels for reapers, binders, and combines were driven at a fixed driving ratio to the lugged wheel; and the fixed ratio was chosen to give a tangential speed to the periphery of the reel bats that was greater than the ground speed of the harvesting machine.
Because the harvesting speed of horsedrawn harvesting machines varied over a very small range, it was possible to select a driving ratio that would provide sufficient differential velocity between the reel and the ground speed, at minimum ground speed, to effectively convey the cut grain from the cutter bar back onto the conveyor belt without hitting the grain with a velocity that would cause shattering of the grain, at maximum ground speed.
With the advent of tractor-propelled harvesting machines, and the later advent of self-propelled harvesting machines, the range of harvesting speeds was increased greatly. This increase in the range of harvesting speeds brought forth the necessity for a means of changing the ratio of reel velocity to ground speed.
The first improvement was the use of dual drive sprockets having a different number of teeth. A change in the drive ratio between the lugged wheel and the reel was made by changing the drive chain from one sprocket to the other. Later, a variable-speed belt drive was used, with the effective pitch diameter of the pulley or sheave being changed by a hydraulic cylinder. Still later, the mechanical drive to the reel was replaced by a hydraulic motor; and the reel speed was controlled by a manually adjusted valve.
The dual sprocket design was highly unsatisfactory because the varying conditions in some fields require large and frequent changes in ground speeds for efficient harvesting; and it was necessary to stop the harvesting machine in order to change the drive chain from one sprocket to the other.
Both the hydraulically-controlled variable-speed belt drive and the hydraulic motor drive alleviated the necessity of stopping the vehicle to change the reel drive ratio; but both required constant attention from the operator of the harvesting machine to prevent the reel speed from being too slow or too fast.
The present invention alleviates all of the aforementioned problems by electronically sensing ground speed and then driving the reel at a velocity that is greater than the ground speed by a predetermined velocity.
The present invention provides improvements over prior art in three distinct areas: in the drive and control of crop-transporting mechanisms of agricultural harvesting machines, as described above, in electrohydraulic valves, and in electronic controls for electrohydraulic valves.
With regard to electrohydraulic valves, proportional-flow electrohydraulic valves have commonly used such devices as nozzles and flapper valves, with the flapper valve being controlled by an electrical force-motor, to control fluid pressure applied to opposite ends of a valve spool and thereby to selectively position the valve spool. Electrohydraulic valves of this type have been expensive, have been highly sensitive to contamination, and have wasted excessive amounts of power through the flapper nozzles.
In contrast, the present invention provides a proportional-flow electrohydraulic valve that utilizes a valve spool which is positioned by an electrical force-motor for a first or pilot section, and a second section that is connected in series with, and controlled by, the first section. The advantages of the present invention are lower cost, elimination of wasted power because of the elimination of pilot flow requirements, and less sensitivity to contamination by elimination of the small diameter nozzles and small flapper clearances of flapper valve designs.
With regard to electronic controls for electrohydraulic valves, the present invention provides an advance over the prior art by providing a pulse-width-modulated driving voltage whose pulse widths are proportional to an input signal, for driving the electrical force-motor.
The pulse-width-modulated driving voltage results in a dither of the valve spool which effectively eliminates silting and sticking of the valve spool. This elimination of silting and sticking allows the use of lower spool-actuating forces and also results in both more accurate positioning of the pilot spool and more precise control of fluid flow.
The present invention also provides an advance over the prior art of electronic controls for electrohydraulic valves by incorporating an offsetting circuit in the electronic controls. The offsetting circuit is effective to increase the effective value of the pulse-width-modulated driving voltage, about proportionality to an input signal, by a manually-adjustable offset voltage.
By the use of the offset voltage as a null voltage, the pilot section may be spring pressed to a minimum or zero conductance by a predetermined spring load, and yet the output of the electrohydraulic valve may still be directly proportional and linear to the input signal.
Further, by use of an offset voltage which is greater than the null voltage, the offset voltage becomes a basic flow voltage which results in fluid flow rates from the electrohydraulic valve that are greater than direct proportionality and linearity by a predetermined fluid flow rate.
It is this basic flow voltage that is used in the crop-transporting mechanism of the present invention to achieve crop-transporting velocities that are greater than ground-speed velocities by a predetermined velocity.